Series-Fed Monopulse Microstrip Array Antenna With Stripline Quadrature Hybrid Comparator Network

Abstract

Microstrip series-fed weighted arrays have widespread applications in millimeter wave (MMW) radar due to their low profile and light weight. Our study proposes a novel Ka-band compact monopulse radar antenna design with a highly directional 2D series-fed microstrip array antenna. The structure is composed of a symmetrical four quadrant radiation array and an innovative stripline monopulse comparator with two segments. Our novel design applies the stripline in the back-end which considerably reduces the antenna's backward radiation. The shaped patterns in the E and H planes are achieved by tapering patch widths and adjusting the impedance transformer of each subarray. Four half power quadrature hybrids are combined to form 2D monopulse feeding in the back-end. Both parts adopt a simple symmetrical layout that simplifies the design process. The measured reflection coefficients of each port are lower than -10 dB across 34.5 GHz to 35.5 GHz working band meanwhile isolation between these ports are better than 25 dB. Furthermore, the first side lobe level (FSLL) in the sum beam, which is remarkably suppressed by Taylor synthesis design method, achieves about -24 dB both in E and H planes. The measured gain of the sum pattern achieves 25.3 dBi at 35 GHz center frequency, while the nulling depth of the difference patterns in both planes are lower than -30 dB.INDEX TERMS Series-fed planar microstrip array antenna, two dimensional monopulse tracking, Ka-band compact radar, stripline comparator network.

A Compact Monopulse Antenna Array With Suppressed Mutual Coupling Using Broadband Schiffman Phase Shifters

“…In response, the use of 90°, 3 dB hybrid couplers along with 90°delay line phase shifters has become a common way to mimic the performance of 180°hybrid couplers and achieve monopulse functionality [8], [9], [10], [11], [12]. Unfortunately, the inclusion of additional 90°phase shifters introduces undesired dispersion in the monopulse comparator, restricting the 30 dB null bandwidth to less than 6%.…”

“…A broadband multilayer microstrip antenna with ratrace hybrid couplers and parasitic patches over the air gap in the X-band was implemented to increase the realized gain in [7], a four-element antenna with ratrace hybrid couplers was also presented in [11], and, a 1-D electronic beam-scanning monopulse antenna array based on a compact stripline phase-shifter was introduced in [16]. the concept of using stripline phase-shifter is also used to design Series-Fed Monopulse Microstrip Antenna array in [12]. A 4×4 broadband planar microstrip monopulse antenna array with a monopulse comparator in a separate layer has been reported in the C-band, which utilizes dual-layer patches with an air gap to enhance the antenna bandwidth [10].…”

Design of monopulse antenna loaded with Fabry–Perot cavity

“…In addition, the coupling between the antenna array and the feed network has increased, resulting in a decrease in antenna efficiency. A highly directional series feed microstrip array is proposed by Zou et al 16 Its feed network is of stripline structure, and the upper and lower stripline layers are connected with the front‐end and the bottom coaxial feed probe through the metallized hole, respectively. This design can effectively reduce the back lobe level.…”